—52% (Oouchi et al. 2006) and +79% (Sugi et al. 2009) in
the future changes in TC frequency (see Table S1 of Knutson et al. 2010a, b), and between −13 and +17% (Oouchi
et al. 2006) for the changes in TC intensity. The ambiguities
largely appear to arise from factors in the model architecture
and representation of physical processes such as model
resolution, choice of convection parameterization, as well as
model-simulated SST changes. In addition, detecting TCs in
climate models is also apparently a form of modeling
uncertainty (see also Murakami et al. 2012a, b). There is a
low confidence in the climate projections of rising annual
frequency of VSCS (category 4 and above; see Table 8.1) at
the end of twenty-first century in the NIO region (2081–
2100 relative to 1981–2005). However, in a 2° anthropogenic warming scenario, there is a medium-to-high confidence in the projected rise in TC precipitation rates and
intensities for the NIO region (Knutson et al. 2019b).
Murakami et al. (2014) also indicated that future changes
in TC activity in the NIO region have larger dependence on
future changes in thermodynamic factors (e.g., low-level
relative humidity, SST anomalies) than future changes in
dynamic factors (e.g., vertical wind shear, low-level vorticity, mid-level vertical velocities). High-resolution climate
simulations show a scenario of increasing TC frequency by
about 46% in the AS region, while there is a reduction by
31% in the BOB region, and the reduction [rise] is notably
during pre-monsoon [post-monsoon] cyclone season (Murakami et al. 2013). The TC frequency is projected to decline
in the AS and BOB regions during pre-monsoon season
where the frequency change is influenced by aforesaid
dynamical factors, while an east–west contrast (i.e., a
reduction in BOB and rise in AS) is noted during the
post-monsoon season where the future changes in aforesaid
thermodynamic parameters may be of greater importance.
There is also an attribution of southerly surge enhancements
over the western AS and southern BOB regions during the
post-monsoon cyclone season due to active inter-tropical
convergence zone situations to the rising frequency of SCS
in these regions (Mohanty et al. 2012). The reader is also
referred to Walsh et al. (2016) and Knutson et al. (2019a, b)
for a comprehensive documentation of climate change
influences on TCs from various oceanic basins.
The IPCC—AR5 report published in 2014 (IPCC 2014)
enunciates that “the confidence on attribution of changes in
TC activity to human influences still is low owing to inadequate observational evidence and physical understanding of
the anthropogenic drivers of climate and TC activity, i.e.,
there is a low confidence in basin-scale projections of
changes in TC intensity and frequency of all basins.” Various recent studies indicate that the projected changes in
global frequency of TCs will decrease while severe TCs
(categories 4 and above; see Table 8.1) in anthropogenic
warming world exhibit a general rise over the global ocean
basins, but the confidence from the information available till
date is still debatable owing to the limited literature (see also
Table 1 of Knutson et al. 2019a). Hitherto, scientific
investigations only led to various contentions in reference to
anthropogenic climate change and its connections to changes
in TC activity pertinent to NIO region. However, Knutson
et al. (2019a) describe that contribution of anthropogenic
forcing signal to rising severe category TS in the AS region
is rather not just coincidental, but there is a medium confidence based on available investigations till date. The latest
assessment by Knutson et al. (2019b) provides a medium
confidence to projected TC intensity rise and
medium-to-high confidence to TC precipitation intensity in
the NIO basin, while the confidence is yet low for the projected rise in the annual frequency of VSCS during the
twenty-first century.
8.3 Localized Severe Storms
Localized severe weather outbreaks occurring on meso-c
scale (on the spatial scale of 2–20 km, a few hours temporally; Orlankski 1975) in association with high winds, hail,
thunder, lightning, etc., are generally categorized into severe
convective storms. Some examples include thunderstorms,
hail storms, dust storms, etc. Various studies (Manohar and
Kesarkar 2005; Kandalgaonkar et al. 2005; Tyagi 2007;
Kulkarni et al. 2009; Singh et al. 2011) have investigated the
severe storm activity for the Indian region. Cloudbursts are a
special class which falls under the short-lived intensely
precipitating convective storms (see Table 8.1). These are
predominant over the mountainous regions of northern part
of India (Das et al. 2006; Dimri et al. 2017; Deshpande et al.
2018).
Thunderstorms are localized convective storms, which
are more frequent at low latitudes, where there is a greater
expediency of convective overturning occurrences in association with heated low-level atmospheric layers coming in
contact with warm ground or water. Synoptic and meteorological conditions generally favorable for the occurrences
of thunderstorm include conditional and convective instability in the atmosphere, ample supply of moisture at low
levels, strong wind shear, and a dynamical mechanism
(lifting or destabilization by advective processes) to release
the instability present in the atmosphere (e.g., Doswell 2001;
Bhardwaj and Singh 2018). Thunderstorms occur all through
the year in different parts of India; however, their frequency
and intensity are found to be maximum from March to May
owing to prevalence of unstable atmospheric conditions and
high temperatures at lower levels (Tyagi 2007; Singh et al.
2011; Saha et al. 2014; Das 2015b). The thunderstorm
activity generally remains low during the mid-ISM months
(July and August) throughout the country, whereas it is
164
R. K. Vellore et al.
the future changes in TC frequency (see Table S1 of Knutson et al. 2010a, b), and between −13 and +17% (Oouchi
et al. 2006) for the changes in TC intensity. The ambiguities
largely appear to arise from factors in the model architecture
and representation of physical processes such as model
resolution, choice of convection parameterization, as well as
model-simulated SST changes. In addition, detecting TCs in
climate models is also apparently a form of modeling
uncertainty (see also Murakami et al. 2012a, b). There is a
low confidence in the climate projections of rising annual
frequency of VSCS (category 4 and above; see Table 8.1) at
the end of twenty-first century in the NIO region (2081–
2100 relative to 1981–2005). However, in a 2° anthropogenic warming scenario, there is a medium-to-high confidence in the projected rise in TC precipitation rates and
intensities for the NIO region (Knutson et al. 2019b).
Murakami et al. (2014) also indicated that future changes
in TC activity in the NIO region have larger dependence on
future changes in thermodynamic factors (e.g., low-level
relative humidity, SST anomalies) than future changes in
dynamic factors (e.g., vertical wind shear, low-level vorticity, mid-level vertical velocities). High-resolution climate
simulations show a scenario of increasing TC frequency by
about 46% in the AS region, while there is a reduction by
31% in the BOB region, and the reduction [rise] is notably
during pre-monsoon [post-monsoon] cyclone season (Murakami et al. 2013). The TC frequency is projected to decline
in the AS and BOB regions during pre-monsoon season
where the frequency change is influenced by aforesaid
dynamical factors, while an east–west contrast (i.e., a
reduction in BOB and rise in AS) is noted during the
post-monsoon season where the future changes in aforesaid
thermodynamic parameters may be of greater importance.
There is also an attribution of southerly surge enhancements
over the western AS and southern BOB regions during the
post-monsoon cyclone season due to active inter-tropical
convergence zone situations to the rising frequency of SCS
in these regions (Mohanty et al. 2012). The reader is also
referred to Walsh et al. (2016) and Knutson et al. (2019a, b)
for a comprehensive documentation of climate change
influences on TCs from various oceanic basins.
The IPCC—AR5 report published in 2014 (IPCC 2014)
enunciates that “the confidence on attribution of changes in
TC activity to human influences still is low owing to inadequate observational evidence and physical understanding of
the anthropogenic drivers of climate and TC activity, i.e.,
there is a low confidence in basin-scale projections of
changes in TC intensity and frequency of all basins.” Various recent studies indicate that the projected changes in
global frequency of TCs will decrease while severe TCs
(categories 4 and above; see Table 8.1) in anthropogenic
warming world exhibit a general rise over the global ocean
basins, but the confidence from the information available till
date is still debatable owing to the limited literature (see also
Table 1 of Knutson et al. 2019a). Hitherto, scientific
investigations only led to various contentions in reference to
anthropogenic climate change and its connections to changes
in TC activity pertinent to NIO region. However, Knutson
et al. (2019a) describe that contribution of anthropogenic
forcing signal to rising severe category TS in the AS region
is rather not just coincidental, but there is a medium confidence based on available investigations till date. The latest
assessment by Knutson et al. (2019b) provides a medium
confidence to projected TC intensity rise and
medium-to-high confidence to TC precipitation intensity in
the NIO basin, while the confidence is yet low for the projected rise in the annual frequency of VSCS during the
twenty-first century.
8.3 Localized Severe Storms
Localized severe weather outbreaks occurring on meso-c
scale (on the spatial scale of 2–20 km, a few hours temporally; Orlankski 1975) in association with high winds, hail,
thunder, lightning, etc., are generally categorized into severe
convective storms. Some examples include thunderstorms,
hail storms, dust storms, etc. Various studies (Manohar and
Kesarkar 2005; Kandalgaonkar et al. 2005; Tyagi 2007;
Kulkarni et al. 2009; Singh et al. 2011) have investigated the
severe storm activity for the Indian region. Cloudbursts are a
special class which falls under the short-lived intensely
precipitating convective storms (see Table 8.1). These are
predominant over the mountainous regions of northern part
of India (Das et al. 2006; Dimri et al. 2017; Deshpande et al.
2018).
Thunderstorms are localized convective storms, which
are more frequent at low latitudes, where there is a greater
expediency of convective overturning occurrences in association with heated low-level atmospheric layers coming in
contact with warm ground or water. Synoptic and meteorological conditions generally favorable for the occurrences
of thunderstorm include conditional and convective instability in the atmosphere, ample supply of moisture at low
levels, strong wind shear, and a dynamical mechanism
(lifting or destabilization by advective processes) to release
the instability present in the atmosphere (e.g., Doswell 2001;
Bhardwaj and Singh 2018). Thunderstorms occur all through
the year in different parts of India; however, their frequency
and intensity are found to be maximum from March to May
owing to prevalence of unstable atmospheric conditions and
high temperatures at lower levels (Tyagi 2007; Singh et al.
2011; Saha et al. 2014; Das 2015b). The thunderstorm
activity generally remains low during the mid-ISM months
(July and August) throughout the country, whereas it is
164
R. K. Vellore et al.